Quenching apparatus for metals



Sept. 9; 1958 Filed Aug. 26, 1954 W. ADAM, JR

QUENCHING APPARATUS FOR METALS 3 Sheets-Sheet 1 weg;

.JTTORNE YS Sept. 9, 1958 w. ADAM, JR

QUENCHING APPARATUS FOR METALS 3 Sheets-Sheet 5 Filed Aug. 26, 1954 S& Qw FA IN'ENTOR.

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United %rates Parent QUENCHILNG APPARATUS FOR METALS William Adam, Jr., Beaderwood, Pa., E. A. Ginkger executor of said William Adam, Jr., deceased, assignor to Ajax Electric Company, Philadelphia, Pa., a corporation of Pennsylvania Application August 26, 1954, Serial No. 452,391

3 Claims. (Cl. 266-6) The present invention relates to salt baths used for quenching in the heat treatment of steel and other metals.

A purpose of the invention is to increase the quenching power of a quenching salt bath furnace.

A further purpose is to obtain improved cooling by downward flow of molten salt rather than upward flow.

A further purpose is to make a quenching salt bath furnace more effective in the steel critical range of about 1300 to 1000 F.

A further purpose is to withdraw the molten salt from a quenching container in a quenching salt bath furnace through the bottom of the container, and then recirculate the salt through the salt bath. t

A further purpose is to return the molten salt from the quenching container to the salt bath proper preferably near the top of the salt bath at one side of the quenching container and directed downwardly.

A further purpose is to obtain by molten salt a cooling rate comparable to that of agitated oil.

Further purposes appear in the specification and in the claims.

In the drawings l have chosen to illustrate one only of the numerous embodments in which my` invention may appear, selecting the form shown from the standpoints of convenience in illustration, satisfactory operation and clear demonstration of the principles involved.

Fgure 1 is a section of the quenching salt bath furnace of the invention on the line 1--1 of Figure 2.

Fgure 2 is a plan section on the line 2-2 of Figure 1.

Figure 3 is a vertical section on the line 3-3 of Figure 2.

Figure 4 is a fragmentary aXial section through the pump tube showing the pump impellor.

Figure 5 is a curve useful in explaining the invention.

Describing in illustration but not in limitation and referring to the drawings:

The traditional quenching media used in the heat trea'- ment of steel have been oil or water. In recent years advantages have been obtained by quenching in media at elevated temperatures, both from the standpoint of isothermal transformation, and also simply to obtain more effective cooling rates especially in the steel critical range of 1300 to 1000 F., with a View to missing the nose of the S curve or TTT curve.

For these purposes molten salt baths maintained at elevated temperature, usually of the order of about 400 F. have been used for the purpose of quenching carbon and alloy steel and other metals for heat treatment purposes.

In the practice heretofore followed, a quenching container has been placed in the salt bath furnace, usually with the top of the quenching container slightly above the level of the salt bath, and a pump has drawn molten salt in the bottom of the quenching container and expelled it to overfiow the top and then by recirculation to enter the inlet of the pump again.

I have discovered a very unusual effect in connection with the circulation of molten salt in a quenching salt bath which greatly improves the cooling rate, particularly der.

in the steel critical range from about 1000 to 1300 F. I find that if, instead of expelling the molten salt through the top of the quenching container, the circulation of the molten salt is reversed, and the molten salt is drawn in through the top of the quenching container (below the' level of the salt in' the salt bath furnace) and expelled through the bottom, markedly improved cooling rates especially in the steel critical range are obtained. I also find that some further benefit can be obtained if the salt withdrawn the bottom of the container is conveyed to the top of the furnace and then discharged downwardly at the side of the quenching container, with the view to obtaining more thorough stirring of the mass of salt near the bottom of the salt bath, and at the same time avoiding an eXcessively high local level at the point of discharge of the salt.

The improvement in the quenching power of liquid salt by sucking it downward through a quenching container rather than upwardly is so pronounced through the entire range of pump speeds that its value in securing maximum cooling etfect on the work is great. This results in advantages of higher and more uniform hardness and improved physical properties in the steel quenched.

The reasons for these improvements may be attributed to the following:

(l) The downward flow through' an unrestricted orifice results in a much more uniform higher velocty flow without turbulence across the quenching area. This permits a considerably higher velocity of 'salt which means a. greater cooling rate on the peces of work which in turn, means a greater quenching power.

(2) Pump efficency is increased, i. e., a flow of moregallons per minute is Secured because of the decrease of turbulence, both in the quenching container and in the bottom return bend.

(3) The vapor phase is probably of much shorter dura-- tion and less pronounced due to the more uniformfiow.

Considering now the drawing in detail, l illustrate a 'salt bath furnace 20 having a suitable metal pot or refractory linng 21, and desirably heated if necessary by conducting electrodes submerged beneath the level of the salt 22 in the bath, the electrodes not being shown, or by the electrical resistance heater 37 as shown.

A suitable metallic quenching container 23 is placed in the salt bath surrounded by the molten salt, with its upper surface 24 below the level of the salt and open at the top, capable of receiving an object or objects to be quenched. The quenching container has an open hollow interior, and at the bottom converges at 25, suitably in conical form, discharging through a bottom pipe 26 into a return bend pipe 27 which in turn connects at the bottom to a pump cylinder 28 which contains a suitable pump, here a centrifugal impellor 30 having blades 31 suitably symmetrically placed (desirably 60 to the axis) angularly spaced around the impellor and mounted on a shaft 32 which enters at 33 in the top of the pump cylin- The top of the pump cylinder is provided with a return bend pipe 34 which conveys the salt to a position at one side of the quenching container adjacent the top of the salt bath and dscharges it preferably in a downwardly directed stream to one side of the quenching container, which tends to more etfectively stir the salt near the bottom of the furnace and especially at the corners.

The entire recirculating mechanism is mounted in the furnace in any suitable way, desirably on a bracket 35' attached to the pump cylinder and enterng through the top of the furnace. The furnace is provided with a suitable thermostatic control element 36 and a heater 37 for use in adding heat where required.

The impellor 30 may be operated at any one of a wide variety of speeds, very good results being obtained over a range from 400 to 900 R. P. M. and higher and lower 3 speeds -being permissible, suitably from 10 to 5000 R. P. M.

In operation the pump desirably operates continuously to withdraw the molten salt from the bottom of the quenching container and deposit it back intothe salt bath furna'ce at the side of the quenching container and downwardly directed in a stream from a point near the top.

The results obtained ar e best understood by reference to Figure 5 in which the ordinate is temperature in degrees F. and the abscissa is time in seconds. Curve A plotted for 440 R. P. M. -ou the pump, shows the cooling rate obtained for a piece of steel being quenched with the molten salt was circulated in the mechanism of Figures 1 to 4 in the direction used in the prior art, that is out the top. Curve B shows the cooling rate for the same piece of steel in the quenching container when the pump operated at the same speed but was used in accordance with the present invention to draw the molten salt into the top of the quenching container and dischargeit through the bottom. It is to be noted that the cooling rate is considerably improved especially in the range between 1000 and 1300 F.

Curve C is plotted for the cooling of the same steel specmen with the direction of motion of the impellor which discharges the molten salt through the top of the quenching container in the device of Figures 1 to 4'at a pump speed of 830 R. P. M. as compared with'curve D which is plotted to show the cooling of the same steel specmen being quenched with the pump Operating at the same speed in the direction to draw the molten* salt in at the top of the quenching container and out at the bottom. Here again the cooling rate is decidedly im- Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. In a quenching apparatus for metals, a salt bath furnace comprising a chamber having interior space and having content of molten salt inthe interior space, a quenching container within the interior space in spaced relation to the walls of the furnace around the quenching container, the quenching container having an open top accessible all around to the molten salt flow and the quenching container being adapted to be surrounded by the molten salt, in combination with means for pumping molten salt out through the bottom of the quenching container supplying it to the mass of molten salt at the side -but outside the container and causing molten salt to pour in a cascade of molten salt all around over the top edge of the quenching container, whereby a continuous vigorous flow of molten salt is maintained like a waterfall over the circumferential top edge of the quenching container and through the interior of the quenching container and this salt carrying' with it the heat from quenching the work is deposited in the mass of the salt bath around the quenching container.

2. A furnace of claim 1, in which said means for pumping molten salt out of the bottom of the container discharges the salt downwardly into the chamber outside the quenching container.

3. A furnace of claim 1, in which said means for pumping molten salt out of the bottom of the container `conveys the salt from the bottom of the quenching container, up one side and then directs the salt downwardly in the furnace interior outside the quenching container.

References Cited in the file of this patent UNITED STATES PATENTS 1,595,803 Merten Aug. 10, 1926 FOREIGN PATENTS 6o6,734 Great Britain Aug. 19, 1948 OTHER REFERENCES vMaterals and Mthods, March 1947, pages 104, 105. 

